Python 替换 datetime 的默认 __str__ 实现？

Question

Is it a way to replace/customize the default __str__ of datetime?

from datetime import datetime
x = datetime.now() # x can be any date from parameters
print(x) # str(x) returns 2020-10-07 10:38:08.048291 too, but I want a different format

I need to change the default __str__ behave for other functions like json.dump(x, default=str) .

x = 12, 'abc', datetime.now(), 223, ....
json.dump(x, default=str)

Answer 1

I think next is a cleaner un-intrusive approach for your case rather than modifying datetime class's __str__ method. You provide custom convertors for any types you need like datetime , while the rest is tried to be converted to json if not possible then falling back to using str(x) if it is json-unconvertable type (like numpy array in my example).

Try it online!

import json
from datetime import datetime
import numpy as np

obj = {
    'time': datetime.now(),
    'other': [1,2,3],
    'str_conv': np.array([[4,5],[6,7]]),
}

def json_default(x):
    if isinstance(x, datetime):
        return x.strftime('%H:%M:%S')
    else:
        try:
            json.dumps(x)
            return x
        except:
            return str(x)

print(json.dumps(obj, default = json_default))

output

{"time": "18:24:57", "other": [1, 2, 3], "str_conv": "[[4 5]\n [6 7]]"}

Answer 2

You can change the output format using strftime(). It's described here under "Formatting and parsing".